The present invention relates generally to crystal pullers for growing single crystal semiconductor material, and to fluid sealing systems for use in such crystal pullers.
Single crystal semiconductor material, which is the starting material for fabricating many electronic components, is commonly prepared using the Czochralski (“Cz”) method. In this method, polycrystalline semiconductor source material such as polycrystalline silicon (“polysilicon”) is melted in a crucible. Then a seed crystal is lowered into the molten material (often referred to as the melt) and slowly raised to grow a single crystal ingot. As the ingot is grown, an upper end cone is formed by decreasing the pull rate and/or the melt temperature, thereby enlarging the ingot diameter, until a target diameter is reached. Once the target diameter is reached, the cylindrical main body of the ingot is formed by controlling the pull rate and the melt temperature to compensate for the decreasing melt level. Near the end of the growth process but before the crucible becomes empty, the ingot diameter is reduced to form a lower end cone which is separated from the melt to produce a finished ingot of semiconductor material.
To increase throughput of the crystal puller, it is desirable to increase the pull rate “v” at which the crystal is pulled up from the melt and the axial temperature gradient at the solid-liquid interface. Co-assigned U.S. Pat. No. 6,579,362, issued Jun. 17, 2003, and incorporated herein by reference, discloses a heat shield assembly for increasing the pull rate and the axial temperature gradient at the solid-liquid interface. This heat shield assembly includes a cooling shield or heat exchanger including a fluid flow path for carrying cooling water therethrough. It is critical that the cooling water not leak into the crystal puller because water will affect the pressure within the puller and thereby damage the ingot and, if the water leak is severe, damage the crystal puller. Moreover, the pressure maintained within the puller (typically, vacuum pressure) must not be negatively affected by the heat exchanger.